At the age of 2, a pack of monsters attacked Helck's and Cless's village and killed their parents.[1] Cless and Helck headed for the capital to find work, however they were forced to live a life of poverty.[2] At the age of 6, Cless became very ill and Helck has to search for a doctor. The two were found in the snow by Sharuami who called her father, Rafaed, to them. Rafaed had Cless seen by Mikaros, who cured him. From then on, Rafaed took Cless and Heck in and raised them. At the age of 16, he joined the army.[3] At the age of 18, Cless became the leader of the 3rd Infantry.

Cless summoned hyperspace energy under the King's Will.[5] Mikaros also enhanced Cless's power to match Helck's.[6]

A "brotherly quarrel"

As Vamirio and Helck run towards the Human King, they are ambushed by Cless. Vamirio prepared for Cless's attack, but did not counterattack because Cless saw through her plan.[7] Vamirio tells Helck that she will fight Cless, but Helck decides to fight his brother himself, much to the displeasure of Vamirio. Helck tells Cless that he is happy to see that his brother is alive, but states that he will not forgive Cless for hurting his comrade.[8] The two heroes then proceed to clash.

Cless, Alicia, and the winged humans commanded by Human King to attack Mikaros. The Human King then commanded the soldiers to fight Rafaed, but Rafaed manages to escape. Cless chases after Rafaed.

While Vamirio is holding the Warriors of Ruin off, Cless comes to her aid.[9] After noticing Vamirio's condition, Cless decides to take drastic action and attempt to go after Sharuami directly. Unfortunately, Mikaros manages to stop Cless and banishes Cless.[10]

Cless took this advantage to go into hyperspace to kill all of the winged soldiers for them to be resurrected outside hyperspace. Afterwards, he comforts Sharuami before wishing his brother farewell.

As a hero, Cless was powerful enough to defeat Demon King Tooru. Cless quickly rose through the ranks of the army of the Human Kingdom. Cless thinks quickly on his feet in battle and has led multiple successful expeditions against monster nests around the Human Kingdom.

He appears to have gotten even more powerful from the influence of the New World. During their battle, Vamirio stated that Cless is significantly stronger than her.[11] Cless initially seems to have the advantage and even manages to break Helck's sword, but Helck reaffirms his goal to save his brother, which causes Cless to back off.

Master Swordsman: Cless is trained in the skill of the sword by the Human Empire and was mentioned to be possibly stronger and better than Rafaed by Rafaed. He is capable easily defeating multiple Warriors of Ruin enhanced by sacrifices.[14] He specializes in destroying weapons.[15] Cless managed to break the Hero Killer and easily destroy the weapons of Warriors of Ruin.[16][17]

Weapon breaking: Cless's signature skill. While such a skill has been performed by a few others throughout the series, none have been shown to have as much mastery of the skill as Cless. Cless is capable of easily destroying the weapons of Warriors of Ruin, which have been shown to withstand the brute force of Helck.[18][19] Moreover, Cless managed to break the infamous sword, Hero Killer, a sword capable of slaughtering heroes including a berserk Uria, a hero that single-handedly stopped the Warriors of Ruin in the past.[20][21][22]